Infant mortality, the ratio of deaths to live births in the first year of life, was very
high in 1900, as the upper chart shows. About one of every six infants died before
the first birthday. By the end of the century, only one of every 141 infants died
before the first birthday (see page 4).

Much of this improvement predated the introduction of antibiotics and
sophisticated
obstetric methods. The most important factors in the decline of infant mortality
included better nutrition and housing, central heating, pure drinking water,
the shift of births from home to hospital, and the availability of feeding
supplements.
During the second half of the century, antibiotics, immunization, and new
techniques for keeping premature infants alive drove infant mortality still lower.

Diphtheria, measles, and pertussis (whooping cough) were the leading killers of
children early in the century. In 1920, more than 30,000 children died from one
or the other. More than 200,000 cases of diphtheria were reported in 1921,
almost 300,000 cases of pertussis in 1934, and 900,000 cases of measles in 1941.
Many more cases probably went unreported.

By 1960, as the lower chart shows, the death rates for all three diseases had been
reduced to zero. Diphtheria was becoming rare; measles and pertussis were still
common but no longer lethal. By 1995, the incidence of measles and pertussis
had fallen significantly, and not a single case of diphtheria was reported in the
continental United States that year.

Other communicable childhood diseases—rubella (German measles), scarlet
fever, and mumps, for example—followed similar trajectories, first becoming less
dangerous and then all but disappearing. The outbreaks of acute poliomyelitis
that frightened parents throughout the country every summer ended abruptly
when an effective vaccine was developed in the 1950s.